Mid- and Far-Infrared Reflection/Absorption Spectroscopy (IRAS) Studies of NO on Rh Single Crystal Surfaces

The NO/CO reaction over Rh metal in automobile catalytic converters is critical to the control of emissions of these pollutant molecules. As part of a program to determine the elementary mechanism(s) of this reaction, we have been performing mid- and far-infrared reflection/absorption spectroscopic (IRAS) measurements of the adsorption and co-adsorption and co-adsorption of NO and CO on Rh single crystal surfaces. Of particular interest is the low-frequency range of the IRAS spectra where we hoped to observe features due to metal-N stretching and/or bending vibrational motions. In particular, we hoped to obtain information regarding the site-requirements for the dissociation of the NO molecule on various Rh single crystal surfaces. An important result from our earlier work is that the selectivity of the reaction for the two nitrogen-containing products, N2 and N2O, is a strong function of the Rh surface structure. On the basis of ancillary data, we suggested that the location of adsorbed NO and N-atoms (formed from dissociation of adsorbed NO) on various Rh surfaces could, perhaps account for the selectivity differences